Possible enhancement of the first-pass metabolism of phenacetin byingestion of grape juice in Chinese subjects

S. Xiao Dong,1 Z. Zhi Ping,1 W. Zhong Xiao,1 C. Chong Shu,1 C. Fattore,2 G. Gatti,2 S. D’Urso2 &E. Perucca2

1Institute of Clinical Pharmacology, Great Chinese Wall Hospital, Beijing, People’s Republic of China and 2Clinical Pharmacology Unit, University ofPavia, Pavia, Italy

Aims This serendipitous study revealed an unexpected effect of Jufeng grape juiceon the CYP1A2-mediated metabolism of phenacetin. Investigation of the inhibitionof CYP1A2 by grapefruit juice was involved but a translation error led to the grapejuice substitution.Methods Twelve healthy subjects took a single oral dose of phenacetin (900 mg) ontwo randomized occasions together with 200 ml water or grape juice. Plasmaphenacetin and paracetamol concentrations were assessed by h.p.l.c.Results Ingestion of grape juice was associated with reduced plasma phenacetinconcentrations, while paracetamol levels were unaffected. Paracetamol to phenacetinAUC ratios increased from 13.9±3.1 to 24.3±3.8 after ingestion of grape juice.Conclusions These findings suggest enhanced first-pass metabolism of phenacetin,due to CYP1A2 activation by grape juice or to desaturation of CYP1A2 isoenzymessecondary to a slower rate of phenacetin absorption.

Keywords: cytochrome CYP1A2, drug metabolism, grape juice, paracetamol,phenacetin

written informed consent and the protocol was approvedIntroduction

by Ethics Committees at both study sites. The clinicalpart of the work was carried out in the Institute ofConstituents of grapefruit juice inhibit CYP3A4, leading

to decreased first-pass metabolism of a number of Clinical Pharmacology, Great Chinese Wall Hospital,Beijing.substrates of this important cytochrome P450 [1].

CYP1A2 activity may also be inhibited by grapefruit After an overnight fast, each subject received a singleoral dose of phenacetin (3×300 mg capsules) on twojuice [2], but evidence for this remains inconclusive. In

order to investigate this interaction, we designed a study randomized occasions separated by an interval of at least1 week. On one occasion the phenacetin was taken withaimed at assessing the effect of grapefruit juice on the

disposition of phenacetin, a marker of CYP1A2 activity 200 ml water and on the other occasion with 200 mlgrape juice rather than the intended grapefruit juice. The[3, 4]. Erroneous substitution of grape juice for grapefruit

juice led to the serendipitous discovery that ingestion of juice was prepared manually by squeezing fresh Jufengvariety grapes through a cotton gauze, the unbrokengrape juice markedly reduces plasma phenacetin concen-

trations, probably due to enhanced first-pass metabolism. seeds being discarded together with the fruit peel. Afterpreparation, the juice was kept frozen at −30° C for upto 3 months, removed from the freezer 12 h before

Methodsconsumption and left to reach room temperature beforeingestion. The volunteers were allowed no food or drinksTwelve healthy Chinese subjects (mean age 36 years,

range 29–46 years, and mean body weight 60 kg, range for 4 h after dosing. Blood samples were collected for upto 12 h and plasma stored at −30° C before shipping50–72 kg) were studied. Six subjects (three males, three

females) were nonsmokers, and six (three males, three frozen for assay in Pavia within 3 months.Plasma concentrations of phenacetin and metabolicallyfemales) smoked more than 10 cigarettes/day. All gave

derived paracetamol were determined by h.p.l.c [3].Correspondence: Professor E. Perucca, Clinical Pharmacology Unit, University Pharmacokinetic parameters were determined by model-of Pavia, Piazza Botta 10, 27100 Pavia, Italy. Tel: +39-0382-506360, Fax:

independent analysis as previously described [3, 4].+39-0382-22741Received 17 November 1997, accepted 9 July 1999. Phenacetin oral clearance (CLo), an indirect measure

© 1999 Blackwell Science Ltd Br J Clin Pharmacol, 48, 638–640638

Short report

Results

Plasma phenacetin concentrations

Ingestion of grape juice was associated with a markedreduction in plasma phenacetin concentrations and adelay in time to peak concentration (Figure 1). PhenacetinCmax, AUC and half-life were significantly reduced,while CLo values were significantly increased (Table 1).

Since cigarette smoking induces CYP1A2-mediatedphenacetin metabolism [5], nonsmokers and smokerswere compared. Grape juice reduced phenacetin AUCand increased CLo values to a similar extent both in nonsmokers (AUC: from 7.6±2.4 to 4.3±1.6 mg ml−1 h;Clo: from 3.8±1.5 to 6.9±2.1 l h−1 kg−1) and insmokers (AUC: from 2.8±0.9 to 1.2±0.2 mg ml−1 h;Clo: from 8.3±2.2 to 13.1±1.9 l h−1 kg−1), thoughthe difference was statistically significant (P<0.05) onlyin the former.

Metabolically derived paracetamol

Plasma paracetamol levels with or without grape juicewere superimposable apart from a modest delay in timeTime (h)

0 2 6 10

Pla

sma

conc

entr

atio

n (µ

gm

l–1)

8

6

4

2

0

4 8 12

Paracetamol

0 1 3 5

4

3

2

1

0

2 4 6

Phenacetin

to peak (Figure 1 and Table 1). Paracetamol to phenacetinFigure 1 Plasma concentrations (means±s.e. mean) ofphenacetin and metabolically derived paracetamol in 12 subjects molar AUC ratios increased two-fold after ingestion ofafter a 900 mg phenacetin dose taken with (closed symbols) and the juice (from 13.9±3.1 to 24.3±3.8, P<0.01).without (open symbols) grape juice. For calculations of means,undetectable concentrations were taken as equal to the detectionlimit (0.1 mg ml−1). Phenacetin means were not calculated if Discussionmore than eight subjects had undetectable levels. Paracetamol wasalways detectable. The complete absorption and extensive CYP1A2-

mediated presystemic metabolism of phenacetin makes itsoral clearance a good index of CYP1A2 activity [3, 4].Furthermore, potentially short-lived effects on first-passof CYP1A2 activity [3, 4] was calculated as Dose/

AUC(0,2). Results are given as means±s.e.mean. metabolism are reflected in changes in the oral clearanceof phenacetin.Comparisons were made by Student’s t-test for paired

and unpaired data as applicable; tmax values were compared To date, most studies on the metabolic modulators infruit juice on drug metabolism have concerned grapefruit,by Wilcoxon’s rank test.

Table 1 Pharmacokinetic parameters (means±s.e.mean and 95% CI for the differences between the two groups) derived from plasmaconcentrations of phenacetin and metabolically derived paracetamol after a single 900 mg phenacetin dose taken with or without(control) grape juice in 12 healthy subjects.

Phenacetin ParacetamolControl Grape juice 95% CI Control Grape juice 95% CI

Cmax (mg ml−1) 2.4±0.6 1.1±0.4** (−2.1; −0.5) 6.9±0.3 7.1±0.6 (−0.8; 1.3)tmax (h)† 1.5 (1; 3) 2 (2; 3)** 2 (2; 4) 3 (2; 5)t1/2 (h) 0.95±0.07 0.79±0.05* (−0.31; −0.01) 2.64±0.18 2.50±0.14 (−0.55; 0.27)AUC (mg ml−1 h) 5.2±1.4 2.8±0.9** (−3.9; −1.01) 37.6±2.8 38.8±3.0 (−2.4; 4.7)CLo ( l h−1 kg−1) 6.1±1.4 10.0±1.6* (0.3; 7.5)

†Median and range.*P<0.05**P<0.01

© 1999 Blackwell Science Ltd Br J Clin Pharmacol, 48, 638–640 639

S. Xiao Dong et al.

which contains inhibitors of CYP3A4- and, possibly, Since CYP1A2 isoenzymes are involved in themetabolism of a large number of drugs and toxins [9],CYP1A2-mediated drug oxidation [1]. Now serendipitous

substitution of grapefruit juice with grape juice resulted even a transient enhancement of activity by fruit juicemay have clinical consequences.in significantly increased phenacetin oral clearance. Both

reduced absorption or increased first-pass metabolismcould decrease plasma phenacetin concentrations.However, although phenacetin absorption rates were

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© 1999 Blackwell Science Ltd Br J Clin Pharmacol, 48, 638–640640